Re: anhidrosis with PPID, IR, panting, metformin, antihistamines and weather changes

Eleanor Kellon, VMD

Anhidrosis is one of the most frustrating problems to attempt to treat, whether associated with PPID or not.  Temperature regulation occurs in the hypothalamus, where the dopamine producing neurons controlling the pituitary originate and are damaged.  The role of dopamine, however, is unclear and PPID anhidrotic horses certainly don't always respond to pergolide.

Older horses in general, not just with PPID, also are less tolerant of the cold.

When extremes of temperature may be expected, it is still generally best to clip the horse and control comfort with sheets and blankets.  Even if temperature changes are extreme in a 24 hour period you will still have enough time to adjust coverings if you pay attention to the weather reports.

As for the antihistamines causing anhidrosis, I've seen those anecdotal reports too but have to think they are actually coincidental.  Antihistamines have been tried as a therapy for equine anhidrosis (don't work) because of success with some types of anhidrosis in people:

Idiopathic Pure Sudomotor Failure Responding to Oral Antihistamine with Sweating Activities- Full HTML - Acta Dermato-Venereologica - Content


I've had some good results in two horses with anhidrosis using L-arginine to support nitric oxide levels. Nitric oxide has been found to be involved in sweating in humans.  This should NOT be used in a horse that has any infection or inflammation.

Eleanor in PA
EC Co-owner
Feb 2001

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